"With just 10 points separating the three candidates, this is likely to be a very tight—and fiercely fought—campaign right through Election Day, now less than three weeks away," said Steve Greenberg, a spokesman for the Siena Poll.

Interestingly, and in a repeat of another special election in upstate New York, negative advertising by Republicans seems to be backfiring. Scozzafava's unfavorability ratings are rising—they now stand at 32 percent—and the poll found voters less likely to vote for her because of her ads. Most of the television spots are not being produced or funded by the Scozzafava campaign—she is very short on cash—but rather are attacks conceived of and funded by the National Republican Campaign Committee.

The poll surveyed 617 likely voters and has a margin of error of 3.9 percent. The special election will take place Nov. 3, and Greenberg predicted things will get crazier before then.

"Over the coming weeks, voters will likely be inundated with mail and commercials for and against all three candidates," he said. "Millions of dollars will be spent in support of the candidates and millions more will be spent attacking them. With one in six voters still undecided, who these undecided voters choose to support—if they choose to vote at all—will likely determine the outcome of this race. And given how tight the race is, this election may very well be won by a candidate with less than 40 percent of all the votes cast."